To satisfy demands for wireless data traffic having increased since commercialization of 4th-generation (4G) communication systems, efforts have been made to develop improved 5th-generation (5G) communication systems or pre-5G communication systems. For this reason, the 5G communication system or the pre-5G communication system is also called a beyond-4G-network communication system or a post-long term evolution (LTE) system.
To achieve a high data rate, implementation of the 5G communication system in an ultra-high frequency (mmWave) band (e.g., a 60 GHz band) is under consideration. In the 5G communication system, beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), an array antenna, analog beamforming, and large-scale antenna technologies have been discussed to alleviate a propagation path loss and to increase a propagation distance in the ultra-high frequency band.
For system network improvement, in the 5G communication system, techniques such as an evolved small cell, an advanced small cell, a cloud radio access network (RAN), an ultra-dense network, a device to device (D2D) communication, a wireless backhaul, a moving network, cooperative communication, coordinated multi-points (CoMPs), and interference cancellation have been developed.
In the 5G system, advanced coding modulation (ACM) schemes including hybrid frequency-shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC), and advanced access schemes including filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) have been developed.
Internet, which is a human-oriented connectivity network where humans generate and consume information, is now evolving to the internet of things (IoT) where distributed entities, such as things, exchange and process information. The internet of everything (IoE) has also emerged, which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server.
As technology elements, such as sensing technology, wired/wireless communication and network infrastructure, service interface technology, and security technology, have been demanded for IoT implementation, a sensor network, a machine to machine (M2M), machine type communication (MTC), and so forth have been recently researched for connection between things.
Such an IoT environment may provide intelligent internet technology (IT) services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances, advanced medical services, and so forth through convergence and combination between existing IT and various industries.
Thus, various attempts have been made to apply 5G communication systems to IoT networks. For example, 5G communication technologies such as sensor networks, things communication, MTC, etc., have been implemented by schemes such as beamforming, MIMO, array antennas, and so forth. Application of the cloud RAN as the Big Data Processing technology may also be an example of convergence of the 5G technology and the IoT technology.
Meanwhile, the 3rd Generation Partnership Project (3GPP) has established technical standards regarding various service scenarios, service requirements, and technical issues to support an IoT environment. The IoT technology standards are intended to provide the IoT technology that enables various things or objects to have network connectivity and to communicate with one another without human intervention, and have characteristics of providing an energy-efficient terminal having an operating life of at least several years, providing an expanded operating region for supporting communication in indoor and underground conditions, and supporting a low-cost/low-complexity terminal allowing large-scale distribution.
Among conventional communication systems, a global system for mobile communication (GSM) system uses timing advance (TA) to alleviate collision between bursts, which occurs due to a round trip delay during uplink transmission of a terminal. Collision between bursts is a problem in which when a terminal performs synchronization based on a signal received from a base station, bursts transmitted from different terminals in the same radio uplink overlap with each other due to a transmission delay in a downlink and a transmission delay in the uplink.
The terminal performs synchronization using a signal transmitted from the base station and determines an uplink transmission point in time (or timing) based on synchronization information. A transmission timing of a base station signal, estimated by the terminal during synchronization, has a difference of a propagation delay between the base station and the terminal than an actual transmission timing of the base station signal. The terminal attempts initial uplink transmission based on the estimated transmission timing of the base station signal. A reception timing of an initial uplink burst from a terminal at a reception end of the base station is different from a start timing of an uplink radio resource allocated by the base station to the terminal by a propagation delay during synchronization and a propagation delay in uplink burst transmission, that is, by a round trip delay between the base station and the terminal. Thus, the terminal needs to transmit an uplink signal by applying TA to compensate for a transmission delay equaling the round trip delay.
Among conventional communication systems, in the GSM system, a TA value of each terminal is determined by the base station. The base station determines a TA value for a terminal in an initial TA estimation process, and determines and updates a TA of the terminal in a continuous TA procedure. The initial TA estimation process begins with transmission of a packet channel request in an access burst format by the terminal. The base station receives the packet channel request sent from the terminal and estimates a TA of the terminal. Once the base station determines a proper TA value for the terminal, the base station transmits TA information estimated by packet uplink/downlink assignment to the terminal. If obtaining TA information through an assignment message, the terminal transmits data in a normal burst format. If the TA information is not included in the assignment message, the data in the normal burst format may not be transmitted, such that the terminal needs to obtain a TA by transmitting a packet TA/power control message or executing the continuous TA procedure. Thus, if the terminal fails to obtain the TA information, the terminal has to wait for executing the next continuous TA procedure.
In a conventional GSM system, to lessen collision between bursts, a guard interval is included in an access burst format that is a burst format in initial uplink transmission to which TA is not applied, and the guard interval is set longer than a maximum round trip delay, lowering resource use efficiency when compared to the normal burst format.
The terminal in the IoT environment has low mobility, thus having a small TA change, a long data transmission interval, and a small data size, such that a need for continuous update of TA is low, and the terminal in the IoT environment may be subject to various types of propagation environments because of being located in various places such as an indoor or underground place. Conventionally, a communication system has been designed in a propagation environment to which a terminal belongs, and thus a TA determination and update process as in a conventional GSM communication system is not suitable for an IoT environment accommodating large-scale terminals by using limited radio resources.